High-Energy Quantum Chromodynamics in Nuclear Collisions

High-energy quantum chromodynamics (QCD) in nuclear collisions centres on the behaviour of gluons and quarks under extreme conditions of temperature and density. When heavy nuclei collide at relativistic speeds, as at the Relativistic Heavy Ion Collider or the Large Hadron Collider, the intense colour fields give rise to collective phenomena such as gluon saturation and the formation of a strongly coupled quark–gluon plasma. In this regime, parton densities become so large that nonlinear interactions tame the growth of gluon distributions, invoking an effective description known as the colour glass condensate. Experimental signatures range from modifications of jet yields and azimuthal correlations to ridge-like long-range correlations in particle emission. Theoretical advances in transverse-momentum-dependent factorisation and resummed evolution equations now allow precision predictions for observables sensitive to both small momentum fractions (small x) and large transverse momenta. Together, these efforts illuminate the partonic structure of nuclei in three dimensions and bridge the gap between perturbative QCD and emergent collective behaviour, with implications for understanding the early universe and the internal dynamics of cold nuclear matter.

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High-Energy Quantum Chromodynamics in Nuclear Collisions publication trend

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Technical terms

Colour glass condensate: An effective field theory describing high-density gluonic matter in the small-x regime, characterised by classical colour fields with random colour charges “frozen” over short time scales.

Gluon saturation: The regime in which further growth of gluon density at small Bjorken-x is suppressed by nonlinear recombination effects, leading to a dynamical saturation scale Qs.

Transverse-momentum-dependent (TMD) distribution: A parton distribution function that retains information on the transverse momentum of quarks or gluons, crucial for describing detailed momentum correlations in scattering.

Gluon Wigner distribution: A quantum phase-space distribution encoding both transverse spatial and momentum information of gluons inside a hadron.

Sudakov factor: An exponential suppression factor arising from the resummation of soft and collinear radiation, which moderates cross sections at high transverse momentum scales.

References

1. Multi-dimensional hadron structure through the lens of gluon Wigner distribution. Physics Reports (2024).
2. Tomography of ultrarelativistic nuclei with polarized photon-gluon collisions. Science Advances (2023).
3. Back-to-Back Inclusive Dijets in Deep Inelastic Scattering at Small x: Complete NLO Results and Predictions. Physical Review Letters (2024).
4. Unified description of DGLAP, CSS, and BFKL evolution: TMD factorization bridging large and small x. Physical Review D (2024).